VELOCITY OF FLOW IN PIPES.--For various purposes, it is often desirable
to know the mean speed at which acetylene, or any other gas, is passing
through a pipe. If the diameter of the pipe is _d_ inches, its
cross-sectional area is _d^2_ x 0.7854 square inches; and since
there are 1728 cubic inches in 1 cubic foot, that quantity of gas will
occupy in a pipe whose diameter is _d_ inches a length of
1728/(_d^2_ x 0.7854) linear inches or 183/_d^2_^ linear feet.
If the gas is in motion, and the pipe is delivering Q cubic feet per
hour, since there are 3600 seconds of time in one hour, the mean speed of
the gas becomes
183/_d^2_ x Q/3600 = Q/(19 x 7_d^2_) linear feet per second.
This value is interesting in several ways. For instance, taking a rough
average of Le Chatelier's results, the highest speed at which the
explosive wave proceeds in a mixture of acetylene and air is 7 metres or
22 feet per second. Now, even if a pipe is filled with an acetylene-air
mixture of utmost explosibility, an explosion cannot travel backwards
from B to A in that pipe, if the gas is moving from A to B at a speed of
over 22 feet per second. Hence it may be said that no explosion can occur
in a pipe provided
Q/(19.
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